The present invention generally relates to an arrangement for the overfill protection for a container of anesthetic liquid being transferred to a drug reservoir for an anesthetic vaporizer. More specifically, the present invention relates to an overfill protection device that prevents the overfilling of the drug reservoir of a vaporizer for use specifically with an anesthetic liquid having a low boiling point. The filling arrangement prevents the overfill of the drug reservoir due to the increased pressure within the anesthetic liquid storage container relative to the supply of anesthetic liquid contained within the drug reservoir.
During the supply of anesthesia, the gaseous anesthetic agent inhaled by the patient is formed of oxygen, nitrogen, nitrous oxide and an inhalation anesthetic agent. Inhalation anesthetics are typically in liquid form at administration temperatures, and an anesthetic vaporizer is needed to gasify the liquid. Anesthetic vaporizers have a drug reservoir for storing the supply of the agent to be vaporized. The vaporized anesthetic is administered for the patient to inhale by means of a carrier gas flow.
Vaporizer reservoirs are provided with fill conduits and valves by way of which inhalation liquids may be added to the container or, when necessary, drained therefrom. Liquid is added to the vaporizer reservoir by either a filling device that is specifically designed for the anesthetic agent or by directly pouring the anesthetic agent into a filling hopper. It is a characteristic of the filling device that it can only be fixed to the storage container for a desired, single type of an anesthetic liquid to be transferred to the vaporizer. Such filling device is characterized and shown in U.S. Pat. No. 6,585,016, the disclosure of which is incorporated herein by reference.
The filling device, such as shown in the above-identified patent, incorporates a liquid flow conduit and a gas flow conduit. The filling of the drug reservoir for the anesthetic vaporizer is based on the exchange of volume in the vaporizer and the storage container for the anesthetic liquid. When the anesthetic liquid flows into the vaporizer, an equivalent volume of gas flows out of the vaporizer and back into the storage container. Correspondingly, when liquid flows out of the storage container, an equivalent volume of gas flows into it. Typically, the filling of the vaporizer stops if the replacement gas flow is exhausted or blocked.
It is essential for the operation of the vaporizer that the vaporizer drug reservoir is not filled over a maximum limit. If the vaporizer reservoir is overfilled, the result may be that an overly high dose of anesthetic agent is delivered, which may, in the worst case, rapidly cause death. Otherwise, depending upon the vaporizer, the vaporizer may stop vaporizing, which would cause the patient to awaken too early.
Referring to FIGS. 1 and 2, thereshown is a typical filling arrangement between a drug reservoir 10 for an anesthetic vaporizer and a container 12 containing a supply 14 of an anesthetic agent. As illustrated in FIG. 1, a filler 16 is positioned between the container 12 and the drug reservoir 10 to provide a conduit between the container 12 and the open interior 18 of the reservoir 10. In the prior art embodiment shown in FIGS. 1 and 2, the filling system is closed and the anesthetic liquid 14 is not allowed to vaporize to external atmosphere. The filler 16 includes a liquid tube 20 extending from the storage container 12 to the open interior 18 of the reservoir 10. A gas tube 22 also extends from the container 12 to the open interior 18 of the drug reservoir 10.
As illustrated in FIG. 1, when the anesthetic vapor from within the open interior 18 is withdrawn through the discharge tube 24 of the vaporizer and administered to the patient, the level of the anesthetic agent 26 falls below the inlet end 28 of the gas tube 22. Since the supply of anesthetic agent 14 contained within the storage container 12 is typically at the same pressure as the anesthetic agent 26 within the reservoir 18, gas travels from the drug reservoir 18 through the gas tube 22 and displaces the anesthetic agent 14 from within the storage container 12 through the liquid tube 20. This process continues until the level of the anesthetic agent 26 within the open interior 18 rises above the inlet end 28 of the gas tube 22. When the inlet end 28 is covered, no additional gas can flow back to the storage container 12 and filling of the drug reservoir 10 is halted. As can be seen in FIG. 2, the inlet end 28 of the gas tube 22 is well below the inlet end 30 of the discharge tube 22 to prevent the flow of the anesthetic agent 26 directly into the discharge tube 24.
Presently, the filler 16 includes either keyed elements or a color coding to insure that only a desired type of anesthetic agent is used with the filling arrangement. Thus, the storage container 12 can be connected only to a filling device suitable for the particular anesthetic agent being delivered.
Unlike many other anesthetic agents, Desflurane boils at room temperature. When the anesthetic liquid begins to boil, the pressure inside the storage container 12 increases. If the temperature of the anesthetic agent 14 in the storage container 12 exceeds the temperature of the anesthetic agent 26 contained within the drug reservoir, the pressure in the storage container 12 can cause the level of the anesthetic agent 26 within the reservoir 10 to continue to rise even though the inlet end 28 of the gas tube is covered and no vapor is flowing back into the supply container 12. In the worst case, the pressure of the Desflurane contained within the storage container 12 may cause the level of the anesthetic agent within the drug reservoir 10 to flow to the dosing device, thus causing malfunction in the entire anesthesia device. Therefore, a need exists for an arrangement for preventing the overflow of an anesthetic liquid into the liquid container of an anesthetic vaporizer, particularly when the anesthetic agent has a low boiling point.
The present invention is a filling system for use between an anesthetic storage container and an anesthetic vaporizer having a drug reservoir. The filling system of the present invention is useful in transferring a liquid anesthetic agent between the anesthetic storage container and the drug reservoir.
The filling system includes a filling device that is positioned between the drug reservoir for the vaporizer and the anesthetic storage container. The filling device includes at least one filling conduit that allows the liquid anesthetic agent to pass from the anesthetic storage container to the drug reservoir. Additionally, the filling conduit allows a flow of replenishment gas to pass from the drug reservoir back into the anesthetic storage container.
The filling conduit includes a filling opening that allows the filling conduit to empty into the drug reservoir. The filling opening provides the lone passageway for both the anesthetic agent and replenishment gas to pass between the storage container and the drug reservoir.
The filling system of the present invention includes a closing valve that is operatively positioned adjacent to the flow opening and is movable between an open position and a closed position. When the closing valve is in the closed position, the closing valve prevents the flow of the anesthetic liquid from the anesthetic storage container into the drug reservoir. The closing valve is configured to move between the open and closed positions based on the level of the anesthetic agent within the drug reservoir. Thus, the closing valve controls the flow of anesthetic agent based upon the amount of anesthetic agent within the drug reservoir, rather than based upon the flow of replacement gas between the anesthetic agent in the anesthetic storage container and the drug reservoir.
The closing valve of the present invention includes a float that is freely movable as the level of the anesthetic agent rises and falls within the drug reservoir. Specifically, the float is pivotally mounted to a wall of the drug reservoir such that as the drug level rises, the float pivots both upward and away from the flow opening.
The closing valve includes a support shaft that is mounted to the float and extends through the flow opening. The support shaft includes an expanded head and a sealing ring. When the float rises with the level of anesthetic agent within the drug reservoir, the sealing ring covers the flow opening and prevents the flow of any additional anesthetic agent into the drug reservoir when the level of the anesthetic in the drug reservoir reaches a desired level. As the anesthetic agent is withdrawn from the drug reservoir, the level of the anesthetic agent decreases and the float pivots downward and toward the flow opening to move the sealing ring away from the flow opening. As the sealing ring moves away from the flow opening, anesthetic agent is again allowed to flow into the drug reservoir.
One advantage of the present invention is the ability of the filling system to prevent the overfilling of the drug reservoir, particularly when the drug reservoir is being used with an anesthetic agent having a low boiling point, such as Desflurane. The filling system of the present invention relies upon the level of the liquid in the drug reservoir to open and close a valve, rather than relying upon the flow of a replacement gas. The closing valve eliminates the potential danger caused by the pressure differential between the anesthetic agent within a storage container and the anesthetic agent within the drug reservoir. The arrangement thus prevents overfilling when there is a temperature difference between the anesthetic storage container and the drug reservoir.